You may be tired of talking about A/C but you can use 134a but it has limitations. The main problem is it can't handle any moisture in the system and I do mean it can't handle any moisture so you need to do a deep vac for 1 to 2 hours. 8 oz of oil is good and I usually poor some in the compressor and some in the hoses. Too much oil is not good. The second big limitation is the size of the condenser and evaporator needs to be bigger to accommodate for the lower efficiency of 134a. High pressure is also a big concern for 134a so don't overcharge. If you are using cans, I add 1 can and see the vent temps, add another can and see the vent temp. After two or three cans you should drive and allow the system to stabilize. I have never added more than 5 cans of 134a.

Now, for two at least two years I have not used 134a due to its limitations and lack of flexibility with it. I have had more system failures once you mess with the factory charge. For factory installed cars with 134a I use a refrigerant called ES12a or Envirosafe 12a. It works great and is very tolerant of most oils although a good flush and adding new oil is always best for a long term use. I have used freeze 12 and do find that many times in older cars with (suction throttle valves using r12) instead of the standard expansion valve, freeze 12 will work better because it runs a higher pressure than ES12a. With the many ford type orifice valves the freeze 12 works better too but then I have had good luck with ES12a. In general I plan to never use 134a again, as I will use mainly ES12a and Freeze 12. This is an opinion so I am not saying if someone wants to use 134a you are wrong because it will work well in a car designed for it but if you are converting to an older r12 system, you most likely will not be happy with 134a. I buy freeze 12 and ES12a on ebay by the case and it is about the same price of 134a.

I converted my '75 GMC (SBC 350) using a new Valeo compressor and an aluminum parallel flow condenser from Arizona Mobile Air. I also used a smaller orifice (Ford Blue) and replaced all the hoses with new barrier hoses. I added a high pressure cutoff that kicks in at about 300 psi. I used PAG oil that was pre-loaded in the new compressor. The original evaporator was cleaned with A/C flush, and the accumulator was replaced. I am using a stock steel fan with an HD thermal clutch, and the stock fan shroud.

My system works best when charged with R134 to 75% of the original R12 charge. With this combo my vent temps are about 35 degrees with an outside temp of about 85-90 degrees.

Bruce

Although I now reside in Oregon I am originally from the southeast. I worked in a shop in Albany Ga. for almost 4 years which specialized in A/C repair The steps you took in converting your system are almost exactly the same as would be performed at that location. 75% of R-12 charge capacity,pag oil upgraded hoses and condenser and the KEY to your extremely low outlet temps "THE BLUE FORD ORIFICE"
In case some of you dont know the summer in southwest Ga. is 95-100+ and 90% humidity (at least)
I just wanted to let you know it's nice as an auto tech to finally see someone do the job right!
My Hat's off to you.

As for the ones who claim freeze 12 and other blended type refigerants are superior to R-134A... I ask you this. Do you think that you are smarter than every Automobile engineer in the WORLD? (as far as I know, there are no auto manufacturers using anything other than R-134A) Why?

Just a word of advice if you're going to use refrigerants other then R-134A or R-12. If you have to have your A/C serviced by a professional please let him know you've put something other than the recommended refrigerant in the vehicle. One big reason is that the dog refrigerants will ruin a professional A/C recovery/recycling machine requiring expensive repair to get them working properly again. I'm fortunate enough to own a refrigerant tester and I usually test the refrigerant to make sure it's either R-134A or R-12 before I service a system. If the reading on my tester comes up "refrigerant unknown" I close the hood and wish the customer good luck. I'm waiting to have my R-134A servicing machine repaired now because someone put some mutt refrigerant in his A/C system and I didn't take the time to test the refrigerant before I connected to the system. Somewhere along the line he probably saved himself $50 and now it's probably going to cost me $1000 to get my machine repaired. So if you use one of the blends or substitutes please plainly mark under the hood somewhere that you have.

I have been using ES-12a for a couple years now.. i used to use a variant called HC-12a, my dad and I have used HC-12a for many years.. he has run it for close to 20 years in his 69 GTO without issues and still does...

I dont let anyone service the Air-Conditioners on my cars but me, thats just how I am, im very picky about being able to see my breath in a car on 95 degree humid days... my daily drivers i typically dont touch the A/C till its out of warranty... if I keep them that long.. seems most times I buy a new daily driver every year or two at the most...

I have sold a couple of my older cars over the years and place the sticker under the hood as to whats in it...

R-134a works great if you have designed the system from the ground up to use it... such as in a streetrod where you are running vintage-air or something such.. but in my case I typically have bought older cars that had factory A/C or if they didnt, I installed a system to surely look like factory A/C which means using the factory evaporator and expansion system...

my current project is this way... factory evaporator, accumulator, and orifice tube, with all new linesets, sanden compressor, and aluminum parallel flow condensor. and ES-12a, it cools twice as good as I remember these cars cooling when they were original....

it should be noted that using ES-12a, HC-12a, or any other Hydrocarbon based refrigerant is nor approved by the EPA or any other agency due to its flammability... R-134a is flammable under pressure however not at 0 pressure... but then many of our hotrods are running high pressure fuel injection systems under our hoods that werent factory designed / installed to be there either so i dont worry about a couple lbs of refrigerant....

I tested this flammability by accident one day in an older cadillac I had.. I was hit head on at highway speed on a hot day... my A/C was on High which meant my condensor was full of liquid HC-12a, the car was pushed back a good 2-3 feet from its normal length.. the condensor smashed immediately and no fire.... at least not on my cadi... the other guys car slid around and caught fire a minute or 2 later.......

but the main thing here is if anyone else works on your A/C they need to know whats in there... the other thing with Blends or ES-12a, HC-12a etc is they need to be charged as a liquid... and also as such if you get a leak and lose a partial charge using these other refrigerants you cannot just top-off... you need to completely evacuate and recharge as you may have lost only one part of the blend...

remember A/C systems dont "use up" or "consume" refrigerant... it just goes around in circles like your tranny fluid... if the refrigerant is low - its because there's a Leak pure and simple...

design your A/C from the ground up and you will have COLD AIR no matter which refrigerant you choose as long as you design for it....

there are things you can do to help also like make sure you have good air flow across the condensor... hotrod air and others make pulley sets that will spin the compressor faster on the belt drive which will help at idle... if you are gonna hotrod at High RPM kick the A/C off... the Sanden type compressors are designed for 134a so they will work better with the higher pressures.. whereas the older frigidaire and tecumseh units may fail under high load conditions... GM R4 radial compressors dont like anything you put in there but R-12 so I stay away from those...

like has been said before Too much oil will slug down a system.. oil doesnt change states its a liquid all the time - too much is tough on the compressor and will greatly decrease system capacity...

vacuum operated heater control valves are a great thing.. if your car doesnt have one install it... in most GM and ford cars for sure the valve closes when the A/C is on MAX or the hot/cold lever is full cold.. why does this help? the air mix doors are notorious for being leaky which means you will be pushing a small amount of air over the heater core even when you are in full cold position... stop the hot water from going through the core and this air bleed wont matter much.. otherwise you are mixing in a little heat when you dont want it..
-Christopher

As for the ones who claim freeze 12 and other blended type refigerants are superior to R-134A... I ask you this. Do you think that you are smarter than every Automobile engineer in the WORLD? (as far as I know, there are no auto manufacturers using anything other than R-134A) Why?

Auto manufacturers are MANDATED BY THE FEDERAL GOVERNMENT to use R-134. Do some research and you will find out it is a policital football that the big $$ lobbyists got passed.

My system works best when charged with R134 to 75% of the original R12 charge. With this combo my vent temps are about 35 degrees with an outside temp of about 85-90 degrees.

Bruce

This is a very good thread. Thanks to all you guys for your information.

A serious question?
Are you saying that on a 90* day running the system on (MAX) recircuated cooled cabin air the outlet temp eventually gets down to 35*?

Or are you saying that 90* inlet air is actually cooled to 35* outlet temp? a 55* drop in one pass across the evaporator? That is superior!!
What is the delta drop (degrees of drop) across the evaporator core itself and at what rpm/ambient/etc. ?

Seems like here today at 95*+ getting a one pass vent temp down to 60* is a real challenge.

The biggest cooling challenge at 95* is getting the outlet temp cool enough when putzing around town. What you get after 20 minutes at 60 mph isn't that important.

Can any of you give good delta drop information for the systems you work with?

This is a very good thread.
Thanks to all you guys for your information.

When I measured the temperature of air exiting the dash vents, the cheap thermometer from Autozone showed between 35 and 40 degrees. The truck was inside a garage bay (shade), hood open and running at a fast idle of 1200-1500 RPM (max air flow), recirculated air on high blower speed, and engine hot enough so the clutch fan should have been fully engaged. The temp sensor in my evaporator is supposed to cut off the compressor at about 35-40 degrees to prevent freezing, and it seemed to be working that way. I didn't make any point to measure a one pass delta across the evaporator.

I clipped the thermometer on the vent and left it there for a few days while driving the truck, and most times the vent temps were about 40 degrees. I never measured how long it took to get down to that temp, but it didn't seem to take very long. My truck is a standard cab, so the volume of air to cool is fairly small.

I think one factor that helped was that I had space for a big aluminum parallel flow condenser. I used one that is about 15x30, which is bigger than you can use in most cars. I also used a new Seltec compressor, which is probably a more efficient design than the old GM A6 compressor I took off.

The biggest stroke of luck I had was to find an AC parts place that would make the new hoses and help me fit them to the truck. I parked in front of the parts store and the guy came out and checked all the connector sizes. He then measured each barrier hose and cut them to fit. The fitting on the evaporator was an odd size (big fitting, small hose diameter), so he had to braze the old one to a new one to adapt sizes. He also went through his stock of accumulators to find one with connectors oriented to work better with the new hose routing. He also sold me the high pressure cutoff switch and added a fitting for it to one of the hose connectors.

Bruce,
You have a good system.
While driving on MAX, switch to normal AC allowing air from the cowl to come in and see what the vent temp increases to.
Then hold the thermometer out the window and see what the ambient temp is. That will give you a good estimate of the delta drop across the coil, at least while driving at speed. Fast idle standing still will not drop as much obviously.

I've made an effort this week to look at condensers in the new vehicles and some of those trucks are humongous. (but won't fit in my rod)

If your system was engineered for R12, then it will not perform to the same capacity with R134, it is that simple. You can only strive for acceptable unless you wish to start swapping parts around. I would deal with the excessive charge you are displaying at the moment.

With your gauge pack hooked up, and your car running, read what the low pressure gauge is showing. The gauge needle will indicate the pressure and temperature on the scale. Look at the temperature for that pressure. Next use a thermometer and measure the temperature of any metal part of the plumbing after the orifice. Subtract the two temperatures and find the difference. It should be around 15 degrees. This is called "Super-heat".

Any larger number that that shows that you need to add more refrigerant as the system is starved, especially if your high side pressures seem low and your not realizing enough cooling.

Any lower number than 15 degrees means there is too much refrigerant and you run the chance of slugging your compressor with liquid refrigerant. This detracts from the life of the compressor... parts break! Watch the pressures on the low side!

Oil is always removed and new oil that is compatible with the new refrigerant must be used! Refrigerant oil does not lube the compressor until it combines with its proper refrigerant, and until it is mixed... it possesses no properties of a lubricant! You are going to want your compressor properly lubed, trust me on this.

Unless you have vacuumed down your system deep enough and removed all traces of water vapor (moisture), the temperatures you get on your gauge pack will not be correct. The pressure and temperature correlation only works if you are measuring pure unadulterated refrigerant at any given pressure.

If you cannot get the performance you are looking for with the proper super heat across your existing evaporator and your high side pressures are in range, try changing out to a larger condenser coil.

Change out the orifice to a larger one if excessive low side pressures do not lead to a reduction in super heat measurements. You may have to fiddle with stuff to get the performance you want.

Like I said, these systems are engineered to work around a specific refrigerant type. A drop-in refrigerant swap does not exist yet.

Also you state that even though the proper super heat temp drop exists that the system might need a bigger condenser. The proper 15* drop is still 15* drop regardless of condenser, isn't it? If not please explain the difference.

It's been a long time since I studied this, but I recall that if the A/C gets too cold you'll get frost inside of the lines thereby plugging the system. A/C systems are designed to shut off before that happens. For example, on older Chrysler products sometimes the air coming out of the vents would reach 35 degrees. When that happened you knew the system was malfunctioning because it should have shut off when the air coming out of the vents was in the middle 40 degree range. Those may not be the exact temps, but that's the gist of it.

It's been a long time since I studied this, but I recall that if the A/C gets too cold you'll get frost inside of the lines thereby plugging the system. A/C systems are designed to shut off before that happens. For example, on older Chrysler products sometimes the air coming out of the vents would reach 35 degrees. When that happened you knew the system was malfunctioning because it should have shut off when the air coming out of the vents was in the middle 40 degree range. Those may not be the exact temps, but that's the gist of it.

Isn't frost moisture?
What about the dessicant and vacuuming the system?
How would "freon" itself freeze up inside of a hose?
Even my '63 system date tagged Aug. '63 cuts off at 36* coil temp to prevent the evaporator condensation from freezing into an iceberg.

Also you state that even though the proper super heat temp drop exists that the system might need a bigger condenser. The proper 15* drop is still 15* drop regardless of condenser, isn't it? If not please explain the difference.

Too cold is a bad thing because as it was explained by the last poster, the evaporator coil fins will freeze the condensate (moisture from air humidity), blocking air flow. The lack of airflow through the fins does bad things... the refrigerant will not be able to absorb any heat from inside the vehicle and will not rise the magical 15 degrees. It it does not rise 15 degrees, that means it will be returning to the compressor as a liquid. Liquids cannot compress, and your compressor will tell you so.. OUCH!

All gauge packs have a needle to indicate the pressure readings. The face of the gauge is graduated into meaningful data with a series of scales. Most have scales for R12, R22 and R134a. If you look close, one of the scales is for temperature. When your gauge pack is in operation, the needle will be pointing to a pressure. If you look at that reading on the temperature scale instead of the pressure scale,you will have the numbers that you need for the temperature at that pressure. Temperatures and pressures are directly related. When one changes, the other follows. Easy. If you look closely at the pix, you can see it has scales for different refrigerants and temperature scale as well. (sorry for the cruddy pix,it was the best I could find). The Black scale shows pressure, and the other colored scales are showing the temperatures of their respective refrigerants... you have to look closely to see.

Measuring super heat is easy, a cheap A/c thermometer is standard for this. Use the hand held thermometer to measure the temp of the refrigerant before it goes into the evaporator coil, use the low side gauge on the gauge pack to measure the heat after it passes through the evaporator. Easy to do.

R134a is not as good as R12, the pressure at which it turns from a liquid state into a gas is different from R12. If there is a pressure difference at which this happens, and pressure and temp are directly related, then there will also be a temperature difference at which this happens.

Think about how little cooling you will get if the refrigerant attempting to take heat out of the passenger compartment is only 10 degrees different in temperature from the air in the compartment! This can happen and still show the magical 15 degree superheat. A larger Condenser coil will shead more heat & lowers the temp of the refrigerant going to the orifice & evaporator coil. The condenser coil has to do two things; not only shed the heat the refrigerant picked up from the passenger compartment, it has to shed the heat of compression as well. Changing the gas back into a liquid will add plenty of heat!!

I hope this is not too wordy & helps you. I tried to not get to technical with my explanation & just serve up the info you need.

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